In order to better understand the object and scope of the present invention, it is convenient to describe the closest known prior art regarding the use of facilities or silos for grain storing and drying, as well as the commonly used moisture control and temporary storage procedures of the harvested grain.
In the present specification the terms “moisture” or “humidity” may be used interchangeably, but preferably the former is applied to solid products and the latter to gases, particularly air.
In principle, the inventors of the present invention have observed a noticeable lack of offer in the market concerning facilities for grain moisture conditioning with natural air and/or low temperature. In general, they have observed that the facilities currently available in the market are not especially suited for different climatic zones, they are not especially designed for easy cleaning and access by operators and do not provide duty cycles prioritizing a gentler grain treatment in order to better preserve its qualities, especially when it comes to conditioning high value grains, at the expense of a slower drying speed. They have also observed that there is still a need of process optimization, in order to obtain a more economically profitable process with lower operating temperatures (prioritizing grain quality) compared to grain dryers currently available in the market.
The purpose of grain moisture conditioning or control facilities is to bring and maintain the grain moisture content within a commercially and technically acceptable range. In this regard, it may be possible both to provide as well as to remove moisture therefrom in order to reach the optimal moisture percentage, however, typically the most common task is to reduce the moisture content in the grain, which usually comes from harvest with an excess moisture regarding commercial and conservational standards. As mentioned above, this type of facility is known to those skilled in the art simply as “grain dryers” including facilities that only allow reduction of grain moisture. Moreover, those that can also increase and/or homogenize the moisture content in the grain mass are known as conditioning systems. Therefore, for all practical purposes the term “grain dryer” can be understood as also referring to a grain moisture conditioner or regulator, as is apparent to a person skilled in the art.
Grain dryers can be classified as high temperature, intermediate temperature and low temperature dryers. High temperature dryers are the most widespread in the market, and consist of drying columns or chambers, vertically arranged (towers) in which the moist grain enters through the top and the dry grain exits through the bottom. Typically these are high drying capacity dryers, but do not prioritize grain quality. Low temperature dryers generally consist of a silo with special characteristics, where the drying/conditioning takes place slowly and uniformly with air at room temperature or heated slightly above room temperature. These dryers/conditioners are known for their excellent drying quality.
Constructively, grain dryers and grain drying facilities using metal silos are usually of the raised-on-columns type, these being the smallest in size, processing and storage capacity; or of the type using larger metal silos, which are usually supported on the ground, after a civil engineering work that serves as a support and floor for the silo bottom structure, included in said civil engineering work the creation of a double-decker floor and a possible inlaid pipe design and conduits needed for its operation.
Broadly speaking, a typical grain drying process starts with loading the grain into the silo. Said grain loading is obtained by lifting and dumping the grain by using, an auger, bucket elevator, wheel, conveyor belt or the like as a means of grain elevation, so as to introduce the grain usually through the center of the silo roof. After placing the bulk material inside the silo, whether said silo is full or not, a variety of fans, exhaust fans, temperature and moisture sensors, heaters and channel opening and closing shutters and other devices are generally connected to the silo in order to circulate an air flow through the grain mass in a more or less continuous way, wherein said air flow draws moisture from the evaporation of water contained in the stored grains. Generally, the construction involves incorporating a double-decker floor into the civil engineering work, or a series of grids, and air blow pipes among other options in order to force a generally upwards air circulation through the stored grains, in order to achieve a moisture removal effect.
However, the control exerted over this air flow process, is as simple as manually turning on and off a fan and manually measuring grain moisture by the staff handling the facility, and as complex as incorporating computers and multiple closed-loop continuous feedback control sensors. Examples of known methods and devices can be found in U.S. Pat. Nos. 4,583,300, 4,750,273, 4,916,830, 5,167,081 and 5,551,168.
It is also known that the air entering the silo is taken from the atmosphere, therefore the temperature and moisture conditions of said inlet air are those of the reigning climate. This implies that the atmospheric air can be as moist as or even moister than the grain mass. In this sense, the options for conditioning said inlet air are to modify its temperature and/or moisture, in order to obtain the moisture absorption effect from the grain mass throughout which said air circulates and produce the drying effect on the grains. It should be noted that increasing the air temperature is a practice that causes the lowering of the air relative humidity and thus increases its moisture from the grain mass absorption power.
In general, the average humidity or moisture of the grain mass required for a certain grain type and a particular intended use is well known to a person skilled in the art. For this reason, the grain drying process seeks to obtain an optimal grain mass average humidity reading, for both conservation and commercialization or industrialization. As an example, popcorn must have an average grain mass moisture content in the order of 14.5% in order to be considered ready for commercialization, and it is therefore understood that higher humidity values such as 18% would not achieve the required quality for its commercialization, thus having to submit the overly moist grains to a drying process in a facility meant for such purpose. In general, in order to obtain the desired moisture content, i.e. the optimum value for conservation and subsequent commercialization, it is necessary to remove moisture from the grain, this being the most common procedure. However, in general, conditioning the grain involves keeping the grain mass within an average moisture range, which may also involve the addition of moisture if said grain mass is too dry. The latter is hardly representative of the grain conditioning processes and can occur in special situations such as in very dry climates or regions and/or a prolonged sun and dry wind exposure of the crop prior to its harvest.
It is for the above mentioned reasons that the inventors of the present invention detected a need for a new type of grain drying facility and an operation procedure allowing the drying of grains with the lowest possible air temperature compared to those currently used in the market, providing a relatively slow drying in order to enhance uniformity in grain drying, maintaining its viability as a seed and decreasing the amount of cracked grains, all this carried out by a novel open-loop predictive control of proven efficiency.